I am trying to subtract a load of dates from an earlier date to end up with seconds which I can then do modular division on with the number of seconds in a sidereal day. This will give me time separation that I can sort to find similar location of points in the celestial sphere. I simply subtracted one of the dates D3 from the earlier date D2 then tried to do the mod division on it and got the same result. I think Iam confused what format these should be in. Or that result is decimal time? Help much appreciated.